(a) Technical Field
The present disclosure relates to a method for forming conductive electrode patterns of a solar cell without increasing electric resistance of the conductive electrode patterns due to the decrease in a line width of the electrode patterns.
(b) Background Art
Generally, solar cells have been fabricated using a different structure depending on the type of solar cell. These different types of solar cells (e.g., silicon solar cells, semiconductor solar cells, OPV, DSC and the like) commonly include the formation of a conductive electrode using generated electrons. The conductive electrode has been widely formed using a screen printing method using a silver (Ag) paste.
However, such a screen printing method employs Ag which is a relatively expensive metal ion, which increases the production cost of solar cells. In particular, since the conductive electrode patterns of a solar cell are formed in a substantially thin line width, the thickness of the conductive electrode patterns should be increased to secure electric conductivity of the conductive electrode patterns. Accordingly, the thickness of the conductive electrode patterns has been currently increased by repeatedly printing an Ag paste on the same area of a silicon substrate or a glass substrate. Therefore, the conventional methods for forming conductive electrode patterns of a solar cell require the repetitive use of Ag, thus increasing the production cost of solar cells.
In addition, since such a screen printing method applies physical pressure to a silicon substrate or a glass substrate, damage may occur to the substrate. In particular, as the need for integration of solar cells and cost reduction has been gradually increased, there are efforts to reduce the unit cost of a silicon substrate based on the production costs of solar cells. To reduce the unit cost of a silicon substrate, the thickness thereof should be decreased.
Furthermore, for dye sensitized solar cells that use a glass substrate, a substantially thin plate substrate with a thickness of about 1 t or less should be used to fit curved surfaces. However, as the thickness of the glass substrate decreases, breakage risk of the glass substrate increases due to physical pressure during the above mentioned screen printing procedure, and thus, the reduction of the thickness of the glass substrate for the formation of a conductive electrode is limited. Currently, when the conductive electrode patterns are formed using the screen printing method, the minimum thickness required to prevent the glass substrate from being damaged due to physical pressures is known to be about 100 to 180 μm.
Moreover, another known method for forming an electrode of a heterojunction solar cell, includes forming a seed layer on the front and the rear of a transparent conducting oxide (TCO) layer after the manufacturing process of a solar cell is progressed before the formation of an electrode, followed by patterning of the seed layer. Another known method discloses a thin film type solar cell and a manufacturing method thereof, which is characterized by forming an optical transmitting thin film on a crystalline silicon wafer to increase optical transmittance and decreasing specific resistance.
Yet another known method includes a transparent electrode for a solar cell that includes a transparent substrate, a photocatalyst layer formed on the transparent substrate with a photocatalyst compound, a metal mesh layer formed on the photocatalyst layer, and a conductive layer formed on the metal mesh layer by coating a conductive material, and a manufacturing method thereof. Other known method disclose that for the fabrication of a solar cell, printing an Ag grid with larger cross sections (e.g., thicker Ag layer) may decrease the series resistance. However, such an approach requires multiple printing steps, thereby not only adding production complexity, but also requiring the consumption of more Ag.
Many attempts to improve efficiency of a silicon solar cell with reducing the cost production have been made, and such a technical trend is commonly applied to the fabrication of compound solar cells, organic photovoltaic (OPV) cells, dye sensitized solar cells (DSC) and the like. In the formation of conductive electrode patterns that are a core component of a solar cell, decreasing a line width of the conductive electrode patterns is an important issue for improving energy conversion efficiency of a solar cell. However, as the line width of the conductive electrode patterns decreases, the electric resistance thereof increases, causing a decrease in electrode performance. Therefore, the conductive electrode patterns of solar cells should satisfy the requirements for a fine line width and high electrical conductivity.
Currently, the screen printing method has been widely used to form the conductive electrode patterns of a solar cell, which prints an Ag paste at an electrode area on a silicon substrate. However, such a screen printing method using an Ag paste requires the use of an expensive metal ion, Ag, thus increasing the production costs of a solar cell. In addition, for a dye sensitized solar cell, an Ag electrode may be contaminated by an electrolyte used therein, which may result in lowering the performance of the solar cell.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.